ACTA MEDICA LITUANICA. 2007. VOLUME 14. No. 1. P. 1–6
© Lietuvos mokslų akademija, 2007 Maternal height and Caesarean section © Lietuvos mokslų akademijos leidykla, 2007
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Short stature is associated with an increased risk of Caesarean deliveries in low risk population Sylvia Kirchengast1, Beda Hartmann2 Institute for Anthropology, University of Vienna, Austria 1
Department of Gynecology and Obstetrics, Hospital of Neunkirchen, Austria 2
Objective. Maternal somatometric characteristics are clearly associated with pregnancy outcome, first of all newborn weight and length. The impact of maternal stature on birth and especially on the mode of delivery, however, is discussed controversially. This study examined the impact of maternal stature on the mode of delivery, in particular on the Caesarean section rate. Methods. In this prospective study, data of 4278 live births at the Viennese University Hospital were analyzed. Since preterm births, maternal age below twenty years, Caesarean delivery on request, breech or transverse presentation and coincident medical diseases such as diabetes mellitus or nephropathy, drug or alcohol abuse, twin birth or IVF were strict exclusion criteria, the study population can be described as a low risk population. Maternal anthropometrics (height, weight, weight gain) and newborn somatic characteristics (birth weight, birth length, head dimensions, APGAR scores) were documented. Binary logistic regression models were used to evaluate the risk factors for Caesarean delivery. Results. The Caesarean section rate was 17.7%. Beside newborn somatometric characteristics, such as head dimensions and birth weight, maternal stature was significantly associated with the rate of caesarean section. With decreasing maternal stature the risk of Caesarean sections increased significantly. Especially among short and very short women (40%). According to binary regression analyses, maternal stature had a significant impact on the mode of delivery, while, in contrast, no significant associations between the mode of delivery and maternal age, prepregnancy weight status, pregnancy weight gain as well as pelvic dimensions were found. Conclusion. Short stature is significantly associated with the risk of Caesarean delivery. Key words: maternal height, infant anthropometrics, Caesarean deliveries
INTRODUCTION The relationship between maternal anthropometric characteristics, first of all maternal weight status and pregnancy weight gain, and pregnancy outcome is well known and has been documented by many authors (1–3). Especially short maternal stature was mentioned to be associated with adverse pregnancy outcome such as high rates of low birth weight newborns and low APGAR scores (4, 5). Furthermore, maternal height has been reported as an obstetric risk factor, since short maternal height may be associated with cephalo-pelvic disproportion (CPD) resulting in obstructed labor (5–7). Correspondence to: Univ. Prof. Dr. Sylvia Kirchengast, Institute for Anthropology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria. E-mail:
[email protected]
Therefore, short maternal stature seems to represent an important risk factor for emergency Caesarean section (8, 9). Steiner et al. (10) described short women, with a stature below 155 cm as high risk patients for Caesarean section even after controlling for labor dystocia. Witter et al. (6) showed that a maternal height less than 157 cm was significantly associated with an increased risk of Caesarean delivery. As the main causes for emergency, Caesarean section in short women, cephalo-pelvic disproportion (CPD) and labor arrest were mentioned (11–17). Although – as to be seen above – a number of studies have reported a correlation between maternal height and the risk of Caesarean section, some authors failed to find any association between maternal height and the mode of delivery (18, 19). Therefore, the present study was aimed to investigate the relationship between maternal stature, pregnancy outcome and the mode of delivery in an
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S. Kirchengast, B. Hartmann
Austrian sample. Since preterm births, a maternal age below twenty years, Caesarean delivery on request, breech or transverse presentation and coincident medical diseases such as diabetes mellitus or nephropathy, drug or alcohol abuse, twin birth or IVF were strict exclusion criteria, the study population can be described as a low risk population. MATERIALS AND METHODS Data set In the present study, data on 4278 births which took place at the University Clinic for Gynecology and Obstetrics in Vienna were analyzed. The data were collected prospectively and altogether the data of 7138 births were collected. In the analyses included were all births which occurred between the 39th and 41rst week of gestation, because only term births of comparable gestational length should be included in analyses. Exclusively nulliparous women ageing between 20 and 41 years whose first prenatal check took place during the eighth week of gestation were enrolled in the present study. Additionally the following inclusion criteria were used: all prenatal check-ups of the mother–child passport completed, the delivery of a single infant without congenital malformations, no registered maternal diseases before and during pregnancy, no hypertension (BP < 150/90 mmHg), no proteinuria, no glucosuria, no pregnancy-related immunization. Furthermore, maternal age below twenty years, Caesarean delivery on request, breech or transverse presentation and coincident medical diseases such as diabetes mellitus or preeclampsia, drug or alcohol abuse, twin birth or IVF were strict exclusion criteria. Therefore, only 4278 births were included in the final analysis. Gestational age was calculated in terms of the number of weeks from the beginning of the last menstrual bleeding to the date of delivery (= duration of amenorrhoea) and by two consecutive ultrasound examinations performed before the 12th week of gestation. All subjects were Caucasians of Austrian or Central European origin. The study was approved by the local bioethical committee. Anthropometric data The following anthropometric data were determined according to the methods described in Knussmann (20): Maternal anthropometrics Stature, prepregnancy weight (PPW), weight at the end of pregnancy (EPW), weight gain during pregnancy (PWG) were determined according to the methods described in Knussmann (20). Stature was determined at the first prenatal visit. Prepregnancy weight was estimated by means of the retrospective method and the first weight determination, which was carried out at the first prenatal visit (8th week of gestation). During the first 13 weeks of gestation a weight gain of only 1.7%
can be assumed. Therefore, combination of the retrospective method and weight determination at the 8th week of gestation seemed to be appropriate in the present study. To determine prepregnancy weight, the mean value of the retrospective estimated weight and the weight at the 8th week of gestation were calculated. Weight gain during pregnancy was calculated by subtraction of prepregnancy weight from body weight at the end of pregnancy. Maternal weight status before pregnancy was described as the body mass index (BMI) (kg/m2). Weight status was classified according to the WHO recommendations (21). Newborn anthropometrics The following parameters were taken directly from the newborn immediately after birth: birth weight, birth length, head circumference, diameter frontooccipitalis, acromial circumference. Birth weight was classified as very low 4000 g. Also, the one- and five-minute APGAR scores for the evaluation of the newborn were determined. Obstetrical characteristics The mode of delivery, spontaneous versus Caesarean section, was documented as an indicator of severe obstetrical complications during birth, because Caesarean sections requested by the mother were excluded from the analysis and therefore only emergency Caesarean sections were included in the present sample. Statistical analysis Statistical analysis was performed by means of SPSS for Windows program Version 11.0. After calculating descriptive statistics (means, SDs), group differences were tested regarding their statistical significance using Student’s t tests. The analysis included the c2 for the linear trend. Additionally, odds ratios were calculated. Binary logistic regressions were computed in order to test the association among maternal stature, prepregnancy body mass as well as newborn anthropometrics and the mode of delivery. Spontaneous delivery was coded as 1 and Caesarean section as 2. RESULTS Mode of delivery Within the present sample, 758 (17.7%) Caesarean sections took place. The most frequent indications for Caesarean delivery were fetal distress (42.8%) and dystocia (37.5%). Maternal and newborn anthropometrics The maternal height distribution is presented in Fig. 1. As to be seen, only less than 10% were shorter than 155 cm. The mean height was 164.1cm (±6.5). The
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Maternal height and Caesarean section
prepregnancy weight status of the majority of women (77.0%) corresponded to the definitions of normal weight (BMI 18.5–24.99); 10.2% of the women exhibited underweight during prepregnancy phase, whereas overweight during prepregnancy phase was found among 13%, however, severe overweight (BMI > 30.00) was only described for 2.4% of the women. Since only term births were included in the present analysis, 92.6% of the newborns corresponded to the definitions of normal
weight (2500–4000 g), 1.6% were classified as low weight (4000 g). Neither maternal prepregnancy weight status nor newborn weight status were significantly associated with the mode of delivery (see Table 1). In contrast, among newborns with an APGAR score below 7 the percentage of Caesarean delivery was extremely high (Table 1).
Fig. 1. Maternal height distribution
Table 1. Maternal and newborn characteristics by mode of delivery, Student’s t tests and c2
Caesarean delivery (n = 819) X (SD) 162.9 (7.1) 59.2(10.5) 22.19 (3.39) 24.8 (2.1) 27.9 (1.9) 3344.8 (435.1) 49.9 (1.9) 36.9 (2.4) 34.4 (1.3) 11.3 (0.7)
Vaginal delivery (n = 3820) X (SD) 164.3 (6.4) 59.9 (9.7) 21.75 (3.21) 24.8 (2.1) 28.0 (2.0) 3335.3 (399.3) 49.8 (1.8) 36.7 (2.2) 34.3 (1.4) 11.3 (08)
Prepregnancy weight status 30.00 kg/m2
8.7% 75.7% 12.7% 2.9%
10.6% 77.0% 10.1% 2.3%
n. s.
Newborn weight status 4000 g
0.0% 2.0% 90.4% 7.6%
0.0% 1.5% 92.7% 5.8%
n. s.
APGAR values < 7 APGAR 1 min (n = 210) APGAR 5 min (n = 34)
43.3% 38.2%
56.7% 61.8%
